The present invention relates to the field of defect inspection devices.
Current automated inspection systems work by having an electronic image sensor or camera take a series of snapshots of the area to be inspected. These snapshots are then processed digitally. The processing typically looks for pixels in the image which deviate significantly from the normal brightness level. Once such a pixel is found, the computer records its location. When enough deviations are found closely grouped together, a defect is declared.
A limitation of current systems is that they process data as a series of still images. These can be captured by strobe photography as the inspected surface moves by the image sensor or they can be photographed when the inspected surface is still. Overlapping images of the surface to be inspected are digitized and processed by a computer. For 100 percent inspection, the overlap must be large enough so that a defect cannot hide in the "crack" between images. Often there is no overlap, or there might even be a space between frames. The result is less than 100 percent inspection of the surface. In order to inspect a large surface in a short time, very high data transfer rates and processing rates are required. For example, if a 0.001 inch wide scratch is unacceptable on a 0.5 inch wide magnetic tape, which is to be inspected at at a rate of five feet per second, a data transfer and processing rate of thirty million pixels per second would be required. Thus, even a modest inspection task can be very burdensome to the computer involved in the inspection process.